Manually operated keyboard switch in a stationary mount with guided shaftway



Aprll 5, 1966 A. c. ERPEL 3,244,847

MANUALLY OPERATED KEYBOARD SWITCH IN A STATIONARY MOUNT WITH GUIDED SHAFTWAY Filed May 22, 1964 5 Sheets-Sheet 1 1'. II n II II n II II n II II II II II II n n n- INVENTOR I ADOLPH C. ERPEL ATTORNEYS Apnl 5, 1966 A. c. ERPEL 3,244,847

MANUALLY OPERATED KEYBOARD SWITCH IN A STATIONARY MOUNT WITH GUIDED SHAFTWAY Filed May 22, 1964 5 Sheets-Sheet 2 25 r-mmnm a a i s n 1 v I a g 1 20 g L |a 2 f F v/ I I ins 2 7 i 1 1 l3 l2 F IG. 3

30 PC. PANEL INVENTOR ADOLPH CERPEL l2 wan-m; 6L1,

ATTORNEYS Aprll 5, 1966 A. c. ERPEL 3,244,847

MANUALLY OPERATED KEYBOARD SWITCH IN A STATIONARY MOUNT WITH GUIDED SHAFTWAY Filed May 22, 1964 3 Sheets-Sheet :5

c- I Iel4; mi/k 1;:- VIBRATION I NODE I I4 FIXED CONTACT TOP POSITION SWITCH CLOSES 44 1% HYSTERESIS BAND/ 33% SWITCH BOTTOMS INVENTOR ADOLPH CERPEL ATTORNEYS MANUAL-LY OPERATED KEYBOARD SWITCH IN A STATIONARY MOUNT WITH GUIDED SHAFT- WAY Adolph C. Erpel', Warrington, Pa., assignor to Navigation Computer Corporation, a" corporation of Pennsylvania Filed May 22, 1964, Ser. No. 369,446 1 Claim. (Cl. 200-159) This invention relates to manually operated pushbutton switches and more particularly to electrical switches which may be employed in keyboards for controlling electronic equipment.

Conventional switches operable manually are susceptible to contact bounce, which makes them unsuitable for direct employment in electronic data processing equipment, for example, as an input to a transistor switching circuit without provision of filtering or buffering-devices.

Thus it is a primaryobject-of the invention to provide a virtually bounceless manually operated switch.

To adapt a switch for operation in an electronic keyboard such. as used on a typewritenit should'have a combination of characteristics in order to meet not only technical operating requirements; but also the touch characteristics demanded by an operator who may operate a keyboard continuously.

Accordingly, it is another object of the invention to provide improved electrical keyboard switches which have an acceptable touch for continuous use without fatigue.

A switch assembly is provided in accordance with this invention that is smooth in operation with little pressure from an operator, even if moved by a glancing stroke from an off-center position at an angle. It has a reasonable range of travel of approximately 7 inch with a constant back pressure of one or two ounces, and makes and breaks contact over a very small range in mid-stroke without any significant snap or back pressure. Thus, it is diificult to jiggle manually or bounce the contacts to produce more than a single closure when depressing and releasing the key.

The switch operates on a novel wiping principle afforded by unc'oiling a loop spring contact wire to brush against a fixed contact with minimum bounce or other contact noise. A long region of wiping of the contacts under forced spring pressure enabled by the coil spring construction feature, serves to eliminate scratch or bounce due to corrosion or denting of the contacts ordinarily encountered in dry contact closures. Any tendency to bounce is further reduced significantly by the placing of the mating fixed contact surface for conductive encounter with the loop spring contact at a nodal vibration region on the coil spring which is not vibrated during switch actuation. In this manner the various desirable features of a low resistance single electrical contact closure and favorable operator touch are combined in a simplified and effective switch mechanism.

The novel switch afiorded by this invention and its principles of operation are accordingly described in detail with reference to the accompanying drawings, wherein:

FIGURE 1 is a broken away perspective view of a contact assembly afforded by the invention,

FIGURE 2 is an elevation view partly in section of the contact assembly of FIGURE 1,

FIGURE 3 is a panel assembly showing the mounting of a plurality of switches on a keyboard,

FIGURE 4 is a partial elevation view of a switch contact assembly constructed in accordance with the invention to have a vibration free contact zone,

FIGURE 5 is a partial elevation view of a switch contact assembly of the invention showing in phantom the wiping action of the contacts, and

1 FIGURE 6 is a diagrammatic sketch illustrating operation-al performance of a switch providedby the invention when manually actuated.

With reference to the-various figures, the switching mechanism is incorporated in a nylon or delren shell 10 which is fused or otherwise affixed to header 11 of the same material, through which two terminals 12, 13 extend. A fixed contact 14. comprising a bent length of spring wire is'nrounted to one terminal post, and a movable contact comprising a spring wire loop- 15 having crossed ends 16, 17 extending therefrom respectively for mounting the contact to terminal 13 and flexing in a direction to expand the coil spring outwardly.

Internal opposing grooves '18 provided in the shell 10 channel a sliding plate 19 for vertical'move'ment between two limiting positions when the plate'19 contacts the bottom and top of the shell case. Extending from the sliding plate 19 is a member having a nylon bumper 20 in constant engagement with the movable end 16 of the spring loop 15 throughout the movement of plate 19.

Although spring loop 15 provides a return force for theslider, it is slight and is supplemented by a coil spring assembly 22 to give the-proper touch. Thus, manual pressure upon blockfi21, will compress spring 22, held onto the extended shaft 24 of the sliding plate 19 by retaining washer 25, to move the end 16 of the spring loop contact 15 into sliding contact with the fixed contact 14 having a portion mounted perpendicular to the path of the loop spring contact surface when flexed.

As may be seen from FIGURES 2 and 3, the header 11 at the bottom of the shell 10 has a slanted surface for permitting direct mounting on a fiat printed circuit panel of a keyboard assembly 31 with contacts 12, 13 extending therethrough. FIGURE 2 additionally displays damping pads 32 which serve to arrest the forked ends of slider plate 19 in its downward position. These pads 32 may be made from semi-rigid urethane which wears well under continuous impact.

The compression spring 22 preferably has a compression force of approximately 60 grams at the point of contact closure, and about 70 grams as the slider 19 reaches the damping pads 32. This combination gives the switch a soft bottoming characteristic to eliminate the feeling of an abrupt stop. Initial movement of the spring 22 occurs at about 50 grams, so that this switch may be produced compatibly with existing requirements for standard keyboard touch.

As shown in FIGURE 4, the antiresonant vibration node region 35 of the spring 15, when actuated by flexing of end 16 with end 17 fixed, is located at the position of the fixed contact 14 to avoid any possibility of bounce or chatter during switching because of resonance of the coil spring 15.

FIGURE 5 illustrates the extended range of wiping motion attained in this switch assembly by use of coil loop 15. The coil loop dimensions permit marker to move over a relatively long distance in wiping contact approximating preferably about three times the distance of the gap between the open contacts as the end 16 of the spring loop is flexed. This is shown by comparison between the phantom downward position and the unflexed solid position. Such wiping operation virtually eliminates all bouncing and scratching in the switch, and the contact regon is plated with precious metals such as Rhodium to offset corrosion and wear and provide low resistance.

In FIGURE 6 the idealistic operation accomplished by the switch construction is diagrammed. As the key is depressed, the contact opening and closing region 44 is in the mid-region of travel of the key block to provide a range of flexing of the spring coil contact 15 before and after conductive contact is made. A very narrow hysteresis band 44 between opening and closing of the contacts 3 results over the wide range of motion. Thus, it is virtually impossible to jiggle the switch manually in this region to cause multiple contact jitter.

Consider the simplified construction features of two simple plastic moldings and a simple metal stamping making up the assembly without any metal to metal parts which require lubrication or which tend to wear. The slide plate 19 may be chromium plated, and it moves in the nylon grooves without lubrication and has almost unlimited life at the slow manual speed of operation encountered in such a switch.

Accordingly the switch construction provided by this invention has ideal bounceless operation which may be used directly into transistor logic circuits without filters or buffers. The wiping action produces clean low resistance contact and very long life. The plastic shell seals the unit from dust, and affords direct mounting on a printed circuit panel. Accordingly, those novel features related to the improved operating characteristics are defined with particularity in the following claim.

I claim:

A switch assembly and stationary mount therefor comprising in combination, switching means having a fixed element including a contact assembly and a movable contact actuating element with a shaft having manual key thereon and adapted to displace the contacts responsive to manual change of position, a housing member enclosing said contact assembly with a hallow shell having a cap on one end with an aperture through which the 7 portion of the movable element with the key extends and a closure member at the other end, structure in the shell I guiding the movable element through a degree of movement longitudinally therethrough to two limiting positions with the movable element contacting the cap and closure member respectively, spring means biasing the movable element to the first limit position mounted about the shaft between the cap and the key outside the shell, and resilient pad means engaging the movable element at the other limiting position at the end of the specified travel range to give a soft bottoming characteristic feel in response to manual depression of the key.

References Cited by the Examiner OTHER REFERENCES Sasse, Ger. App. No. 1,145,689, pub. 4/1963.

ROBERT K. SCHAEFER, Primary Examiner.

KATHLEEN H. CLAFFY, Examiner.

D. SMITH, 1a., Assistant Examiner. 

